Boiler pipe materials and standards
Standards and material for steel pipe are available at carbon, alloy, and stainless steel material.
Carbon steel: ASTM/ASME A/SA 106, ASTM A179, ASTM A192, ASTM/ASME A/SA 210, ASTM A333 Gr 1, 6,7 to Gr 9,
Alloy steel: ASTM/ASME A/SA 213 T1, T2, T5, T9, T11, T12, T22, T91, T92; ASTM A335 P1, P2, P5, P9, P11, P12, P22, P91, P92
Stainless Steel: ASTM A268, ASTM A213, TP304/L, TP316/L, 310S,309S,317,317L,321,321H, and duplex stainless steel material etc.
Common Sizes: OD from 6mm to 1240mm, thickness from 1mm to 50mm
Types: Straight boiler pipe, and U boiler steel pipe for tube exchanger bundle.
These standards specify the classification, size, shape, weight and allowable deviation, technical requirements, inspection and test, packaging, marking and quality certificate of seamless steel tubes for the boiler.
Boiler Pipe Size
Boiler pipe size range complied with the different ASTM standard required. Like ASTM A106 or ASTM 179, 192 etc.
But most of the boiler pipe size is small, outer diameter usually less than 1 1/2” (1/4”, 1/2”, 3/4”, 1” and 1 1/2”). Than 2”, 2 1/2”, 3” and maximum to 4”.
Medium and high-pressure boiler pipe differences
Based on different working temperature, the medium or high-pressure boiler pipe shall be used. Normally classified as below cases:
a. The operation temperature of general boiler pipe is lower than 450℃. The medium pressure boiler pipeline mainly adopts a hot rolling process or cold drawing process.
b. High-pressure boiler pipes are often used in high temperature and high-pressure conditions. Under the action of high-temperature flue gas and steam, the pipe will occur oxidation and corrosion. It is required high-pressure boiler pipe that has high durable strength, high oxidation-corrosion resistance, and good tissue stability.
Boiler Pipe Manufacturing methods
The manufacturing method of medium and high pressure boiler steel pipe is same with the seamless steel pipe, but there are some key manufacturing processes shall be noted:
Fine drawing, surface bright, hot rolling, cold drawn, heat expansion
Heat treatment methods applied in the boiler pipes
Heat treatment is a method of changing the physical properties of high pressure boiler pipe by heating and cooling. Heat treatment can improve the microstructure of high pressure boiler pipe, so as to meet the required physical requirements. Toughness, hardness and wear resistance are obtained by heat treatment. In order to obtain these characteristics, it is necessary to adopt quenching, annealing, tempering and surface hardening.
a. Quenching
Hardening, also called quenching, is that high pressure boiler pipe is heated evenly to the appropriate temperature, then quickly immerse in water or oil for rapid cooling, and cooling in the air or in the freezing zone. So that the high pressure boiler pipe can obtain the required hardness.
b. Tempering
High pressure boiler pipe will become brittle after hardening. And the stress caused by quenching can make the high pressure boiler pipe tapped and broken. The tempering method can be used to eliminate brittleness. Although the hardness of high pressure boiler pipe is lighter reduced, its the toughness can be increased to reduce the brittleness.
c. Annealing
Annealing is the method to eliminate the internal stress of high pressure boiler pipe. The annealing method is that the steel parts need to be heated to the critical temperature, then put in dry ash, lime, asbestos or closed in the furnace, then let it cooling slowly.
The Basic Method of Rust Removal
a. Cleaning
Using the solvent and emulsion to clean the surface of a high-pressure boiler pipe, so as to achieve the purpose of removing oil, grease, dust, lubricant and similar organic matter. But it cannot remove the dust, oxide skin, welding medicine and so on. So it is only as a supplementary method in the anti-corrosion production.
b. Tool
Tool rust removal mainly uses a wire brush and other tools to grind the surface of a high-pressure boiler pipe. It can remove loose or warp of the oxide skin, rust, welding slag and so on. A manual tool can reach the SA2 level, power tool can reach SA3 level. If the iron oxide scale attached to the surface, it cannot reach the anchorage depth required by the anti-corrosion construction.
c. Acid cleaning
High pressure boiler pipe generally adopt chemical and electrolytic methods to do pickling treatment.
d. Spray rust removal
Spray rust removal cannot only remove rust, oxide and dirt completely, but also high pressure boiler pipe can achieve the required uniform roughness under the action of abrasive impact and friction force.
Spay rust removal cannot only expand the physical adsorption on the surface of a high-pressure boiler pipe but also enhance the mechanical adhesion between the anti-corrosion layer and the pipe surface. So spray rust removal is an ideal method of rust removing for pipeline corrosion.